1. Field of the Invention
The invention relates to an engagement securing device, more particularly to an engagement securing device which ensures proper engagement between a motherboard and a central processing unit having a heat sink disposed thereon.
2. Description of the Related Art
With the fast development of computer technology, central processing units (CPU) are now operating at a very high speed, which means increased heat generation. To prevent overheating which may result in undesirable shutdown of the computer or damage to electronic parts, a heat sink is generally disposed on the central processing unit to help dissipate the heat generated thereby.
FIG. 1 shows a central processing unit 82 mounted on a motherboard 81 using the PGA (pin grid array) technique. A heat sink 83 is mounted on an upper side of the central processing unit 82 via screw bolts 86 that pass through a heat sink mounting member 85 and the motherboard 81.
Since the central processing unit 82 has pins 821 extending through and soldered in through holes 812 in the motherboard 81, even if the motherboard 81 is flexed upwardly and downwardly to a predetermined extent during a product reliability test conducted prior to delivery ex-factory or when subjected to a relatively large impact or shock in actual use, the pins 821 will not slip out of the through holes 812 so as not to affect electrical connection. However, if the motherboard 81 is formed by multiple substrate layers, the pins 821 that pass through the through holes 812 are likely to obstruct wiring and take up valuable wiring spaces on the substrate layers. Therefore, other CPU mounting techniques, such as the BGA (ball grid array) technique, have been developed.
Referring to FIGS. 2 to 4, a BGA-packaged central processing unit 92 is electrically connected to an upper surface of a motherboard 91 via arrays of tin balls 97 (best seen in FIGS. 3 and 4) disposed therebetween so as to overcome the wiring problem. However, when the motherboard 91 is subjected to a reliability test or a large impact or shock in actual use, both sides of the motherboard 91 may flex downward excessively, as shown in FIG. 3, so that lateral sides of a heat sink mounting member 95 supporting a heat sink 93 disengage from the upper surface of the motherboard 91. On the other hand, both sides of the motherboard 91 may flex upwardly so that the heat sink mounting member 95 bearing the heat sink 93 disengages from the upper surface of the motherboard 91. In either case, the electrical connection of the tin balls 97 is adversely affected, and the engagement between the heat sink 93 and the motherboard 91 is impaired.
Therefore, the main object of the present invention is to provide an engagement securing device which ensures proper engagement between a motherboard and a central processing unit having a heat sink disposed thereon.
Accordingly, the engagement securing device of the present invention helps maintain proper engagement between a motherboard and a central processing unit of a computer. The motherboard has upper and lower sides opposite to each other in an upright direction. The upper side has a mounting portion and a peripheral portion surrounding the mounting portion. The central processing unit is mounted on the mounting portion. The computer further includes a heat sink disposed on the central processing unit and spaced apart from the mounting portion in the upright direction, and a heat sink mounting member disposed to support the heat sink on the mounting portion. The engagement securing device includes a support member, a first spacer member, a plurality of first inner peripheral portions, a plurality of second inner peripheral portions, a plurality of elongate tightening members, and a plurality of second spacer members. The support member is adapted to be disposed under the motherboard, and has upper and lower surfaces. The upper surface is adapted to be spaced apart from the lower side of the motherboard in the upright direction, and has a supporting portion corresponding to the mounting portion, and a surrounding portion corresponding to the peripheral portion. The upper surface is configured so that the surrounding portion is spaced apart from the lower side of the motherboard by a first length, and so that the supporting portion is spaced apart from the lower side of the motherboard by a second length which is shorter than the first length. The surrounding portion defines a plurality of first tightening holes, each of which extends downwardly through the lower surface. The first spacer member is disposed on the supporting portion on the upper surface, and is adapted to abut against the lower side of the motherboard. The first inner peripheral portions are adapted to be formed in one of the heat sink and the heat sink mounting member. Each of the first inner peripheral portions defines a second tightening hole that is aligned with a respective one of the first tightening holes. The second inner peripheral portions are adapted to be formed in the peripheral portion. Each of the second inner peripheral portions defines a third tightening hole that extends through the upper and lower sides of the motherboard. Each of the elongate tightening members is configured to pass through a respective one of the third tightening holes, and is disposed to bring the surrounding portion to move toward a respective one of the first inner peripheral portions and a respective one of the second inner peripheral portions. The second spacer members are disposed on the upper surface at the surrounding portion. Each of the second spacer members is adapted to abut against the lower side of the motherboard around a respective one of the second inner peripheral portions so as to resist displacement of the surrounding portion toward the second inner peripheral portions, thereby maintaining the first spacer member between the supporting portion and the mounting portion.